Acoustic apparatus



Oct. 4, 1966 J. v. BOUYOUCOS ACOUSTIC APPARATUS Filed April 5, 1965 I I II I II I I 'IIII I IIII I I I I I'II II'I I'I I'I'I'II'I I I' IIII I I I'I II III I I I II I'II II II I III I I I I II I I I I I g N- A mm IWm WIM wM IG IN I I. 9 I? mm II L IN VENTOR. JOH/V V. EOUYOUCOS M K M AGE/VT United States The present invention relates to an acoustic apparatus, and particularly to a hydroacoustic apparatus for generating high energy, short duration impulses or acoustic transients in an underwater medium.

. Unconventional sonaracousticprojectors generate acoustic signals which are usually peak-power limited to the extent that a transmission of a pulse short enough to exihibit the desirable features of a transient signal results in total energy values insuflicient to achieve desirable detection ranges. In order to achieve transient signals of suflicient- 1y high energy levels, it is usually necessary to employ wave shapes which embody predominantly positive pressures over the duration of the signal pulse, since negative pressure excursions are peak limited by cavitation. For example, explosive shots and mechanical impact devices can provide high peak positive pressure values for a short duration with substantially negligible negative pressure excursions. While explosive shots and mechanical impact devices have worked satisfactorily for the purpose intended, they do present such problems as safety hazards and low reliability at the energy levels required.

Accordingly, it is an object of the present invention to provide an improved hydroacoustic impulse generator which produces high energy transient acoustic signals having positive pressure excursions.

It is another object of the present invention to provide an improved underwater acoustic apparatus which is simple, rugged and reliable.

It is yet another object of the present invention to provide a hydroacoustie impulse generator which utilizes the potential energy stored in a sea-pressure head to produce a shock wave front of finite duration and high energy content by converting avai-lable potential energy into kinetic energy from which a shock is produced.

It is a further object of the present invention to provide a hydroacoustic impulse sound generator to produce short duration impulsive signals of high energy content in an underwater environment, the generator having application in high resolution sonars and geophysical apparatus, for example.

The above objects and other objects of the present invention are accomplished by a hydroacoustie impulse generator which takes advantage of the environment at which the generator is located. More specifically the hydroacoustic impulse generator generally operates at substantial depth in a water environment, such as the sea, and utilizes the pressure or potential energy stored in the sea pressure head to derive a shock wave front of finite duration and high energy content.

The generator may include a housing having a cylindrical cavity of a given length opened at one end to the water environment and a piston slidably disposed within the cavity. The piston and cavity define a chamber within the housing. Further included are a clamping means for selectively clamping the piston at the open end of the cylindrical cavity and means for evacuating the chamber to a pressure below the ambient pressure of the water environment to which the housing end is exposed. Also in eluded is a control means connected to the clamping means for selectively releasing the piston.

The invention itself, both as to its organization and method of operation, as well as additional objects and advantages thereof will become more readily apparent from a reading of the following description in connection with the accompanying drawings in which:

FIGS. 1 and 2 are central cross-sectional views of an hydroaeoustic impulse generator in accordance with the invention in different stages of operation.

FIG. 3 is a partially schematic cross-sectional view which illustrates another embodiment of the invention; and

FIG. 4 is a cross-sectional view which illustrates a hydroacoustic impulse generator incorporating a spherical housing.

Referring more particularly to FIGS. 1 and 2, hydroacoustic impulse generator 10 is shown submerged at a given depth in a fluid medium such as the sea or ocean. The hydroacoustic impulse generator 10 comprises a housing 11 having a cylindrical bore 12 and a piston 13 slidably disposed in the cylindrical bore 12 of the housing 11. The housing 11 further includes a horn port-ion 14 at one end 15 of the cylindrical bore 12 and a rear anvil portion 16 enclosing the other end 17 of the cylindrical bore 12 to define a cavity 18. The piston 13 separates the horn portion 14 from the cylindrical cavity 18 which effectively then divides the housing 11 into two regions, an extenal region about the horn portion 14, and an interior region within the housing 11. The horn portion 14 and one face 3 of the piston 13 are contiguous to the fluid medium which has an ambient pressure or pressure head, P of the sea at the given depth at which the hydroacoustic impulse generator 10 may be located. The internal region within the housing 11 is bounded by the piston 13, the rear anvil portion 16, and the cylindrical bore 12 which together define a chamber 19. A high pressure fluid may be selectively introduced into the chamber 19 for moving the piston 13 against the pressure head P and a piston stop 20 on the housing 11. The chamber 19 may be evacuated to a low pressure, P which may be, for example, a partial vacuum in accordance with the invention. The volume of the chamber 19 is at a maximum when the piston 13 is disposed at the piston stop 20 in the open end 15 of the cylindrical bore 12. The maximum volume may be, for example, a liquid volume of liters. The 100 liters would compare approximately to the volume of a right cylinder having a diameter of twenty (20) inches and a length of twenty (20) inches. At a depth of a thousand (1000) feet in sea water, a mass of sea water contained in a volume of 100 liters would possess about 300,000 joules of pressure or potential energy.

The hydroacoustic impulse generator 10 further includes a hydraulic clamping means 21 disposed at the open end 15 of the cylindrical bore 12 proximal to the horn 14. The hydraulic clamping means 21 clamps the piston 13 at the open end 15 of the cylindrical bore 12 in a position which may be referred to as the cocked position.

The clamping means 21 includes a thin cylindrical wall sleeve 23 which may be a separate element of resilient material or an integral part of the housing 11 when the housing 11 is made of a resilient material such as aluminum or steel. The sleeve 23 is defined by the cylindrical bore 12 and an annular chamber 24 encircling the sleeve 23. The sleeve 23 is of a cantilever construction and is resilient and yields to fluid pressure within the annular chamber 24 to effectively decrease the diameter of the cylindrical bore 12 proximal to the open end 15 of the cylindrical bore 12. The effective reduction of the diameter of the cylindrical bore 12 is sufficient to clamp the piston 13 in the cocked position as illustrated in FIG. 1.

Although one type of hydraulic clamping means 21 is shown in the hydroacoustic impulse generator 10 of FIG. 1, other piston clamping means may be used without departing from the invention. For example, mechanical or electro-mechanical means such as a camming or solenoid means, not shown, may be used to controllably clamp the piston 13 in the cocked position. Another hydraulic piston clamping means is illustrated in FIGS. 3 and 4 and will be described in more detail hereinafter.

The hydroacoustic impulse generator may be connected to a pumping means, not shown, for applying hydraulic fluid pressure to the cylindrical bore 12 and to the hydraulic clamping means at inlets and 26 respectively to position and clamp the piston 13 in the cooked position. The pumping means which applies the hydraulic pressure to the chamber 19 may also be used to evacuate 'the cylindrical chamber 19 in the housing 11. The pumping means employed in the hy-droacoustic impulse generator 10 (FIG. 1) is shown in more detail in FIG. 3 connected to another embodiment of a hydroacoustic impulse generator and will be described together with FIG. 3.

In the operation of the hydroacoustic impulse generator 10 the piston 13 is first clamped in the cocked position by the hydraulic clamping means 21. The chamber 19 is then evacuated to a pressure P which may be for example a partial vacuum. The piston 13 can be selectively released from the cooked position by the hydraulic clamping means 21, whereupon the piston 13 is accelerated towards the rear anvil portion 16 of the housing 11 in response to the pressure or pressure head P of the sea. The pressure acting on the piston 13 is the difference in pressure between the pressure head P and the partial vacuum P which exists within the chamber 19. At the moment when the piston 13- impacts with a velocity v at the rear anvil portion 16 of the housing 11, there exists a column of fluid of length l upstream from the piston 13 which also has assumed the velocity v The column of fluid has kinetic energy B as expressed by the equation:

E /2plAv (1) where p is the density of the fluid;

' l is the length of the column of the fluid;

A is the cross sectional area of the cylindrical bore 12;

and v is the velocity of the column of fluid.

where pc is the characteristic impedance of the fluid.

Thus, a pressure disturbance P is produced which propagates down the cylindrical bore 12 and extinguishes the velocity v as it travels outward and leaves behind it a stagnant region of high pressure P the magnitude of which is expressed by Equation 3. When the pressure wave reaches the horn 14 the fluid in the cylindrical bore 12 is now at the elevated high pressure P and has zero particle velocity. The phenomenon which has happened at this particular instant may be likened approximately to the classical shock-tube initial condition where at the time of diaphragm rupture there is a pressure discontinuity between adjacent bodies at rest. The phenomenon just described is unstable and a shock wave front will propagate from the cylindrical bore 12 into the born 14 and be transmitted into the fluid medium surrounding the housing 11.

In addition to the above phenomenon a rarefaction wave will propagate back into the cylindrical bore 12.

This rarefaction wave is reflected at the piston 13 and travels back up the cylindrical bore 12 to the horn 14. If the length l of the cylindrical bore is properly chosen in relation to the bore diameter and horn mount diameter, a double transit of the rarefaction wave in the cylindrical bore 12 will return the contained fluid medium to a quiescent state at the ambient pressure, P of the fluid medium surrounding the hydroacoustic impulse generator 10. The shock front propagating into the surrounding fluid medium will have a pulse length T, approximately as follows:

where T is the pulse length; l is the length of the cylindrical bore 12; and C is the speed of sound in the fluid medium.

The surrounding fluid medium is like a radiation load which has the characteristics of a parallel inductanceresistance (L-R) circuit. Because the radiation load has the characteristics of a parallel inductance-resistance (L-R) circuit, the shape of the output pulse of the hydroacoustic impulse generator 10 takes the form of a steep shock front with a decaying tail. The shape of the tail and the length of the pulse are, in practice, modified to some extent by the residual kinetic energy in the horn and surrounding fluid.

The potential energy of the fluid medium at the given depth can thus be used advantageously to produce strong shocks of finite and controllable pulse duration by the conversion of the potential energy of the sea pressure head first into kinetic energy and then into shock energy. This energy conversion is accomplished entirely within the fluid medium and the shock energy does not have to be transmitted through solid medium or other mechanical device such as typical mechanical impact sources or generators.

The piston 13 may be returned to the cocked position by admitting a high pressure fluid into the cylindrical bore 12 and chamber 19. The piston 13 may then be clamped in cocked position by the hydraulic clamping means 21. The fluid within the chamber 19 may be evacuated again to a partial vacuum. The operation of the hydroacoustic impulse generator 10 is repeatable by suitable control of the fluid pressures in the chamber 19 and the hydraulic clamping means 21, as just described.

Referring now to FIG. 3, another embodiment of the invention is shown in a hydroacoustic impulse generator 30, connected to a signal responsive fluid pressure control means 31 at clamping means inlet line 32 and piston inlet line 33. The signal responsive fluid pressure control means 31 may also be used in the hydroacoustic impulse generator illustrated in FIGS. 1-4- and is shown by way of example for providing a high fluid pressure or a suction for operating the hydroacoustic impulse generator 30 in the fluid medium. The high pressure fluid for the .hydroacoustic impulse generator 30 may be a gas or a liquid.

The signal responsive fluid control means 31 is shown in schematic view in FIG. 3 and may, for example, comprise a fluid pressure and vacuum source 34 which may include a high pressure pump not shown, having a high pressure outlet at 35 for high pressure fluid, and a suction pump, not shown, having an intake connection at 36. A high pressure fluid may be supplied from the high pressure outlet 35 to inlet lines 37 and 37a through a first electrically controlled valve 38 to the piston inlet line 33 of the hydroacoustic impulse generator 30. The fluid pressure and vacuum source 34 also provides a suction at intake 36. A valve 41 controls the suction to the piston inlet line 33. The valves 38 and 41 may be selectively and alternately operated to provide a high pressure or a partial vacuum in the piston inlet line 33. The intake branch line 37a provides a high pressure fluid passage to the clamping means inlet line 32 through a valve 42. A

valve 43 controls the partial vacuum or suction between the intake connection 36 and the clamping means inlet line 32. All the valves, 38. 41, 42 and 43 in the signal response pressure control means 31, are electrically connected to a fluid control circuit 44 and are responsive to electrical control signals from the fluid control circuit 44 for selectively applying a suction or high pressure fluid to the hydroacoustic impulse generator 30 as desired. The fluid control circuit 44 may be located at a remote point from the hydroacoustic impulse generator 30 and may, for example, be mounted in a vehicle such as a ship not shown.

The hydroacoustic impulse generator 30 of FIG. 3 is substantially similar to the hydroacoustic impulse generator of FIGS. 1 and 2, except that the hydroacoustic impulse generator includes a hollow piston 46, coacting with an anvil 47 which is mounted to substantially eliminate the transfer of mechanical shock or vibration to a cylindrical housing 51 of the hydroacoustic impulse generator 30. V

The cylindrical housing 51 of the hydroacoustic impulse generator 30 includes a cylindrical bore 52 which is adapted to receive the anvil 47 and the hollow piston 46 in a slidable relationship. The hollow piston 46 is slidably mounted between the anvil 47 and the cylindrical bore 52. The housing 51 is sealed at one end 53 by a removable end plate 54. The other end 56 of the housing 51 includes an enlarged mouting flange 57 for mounting an acoustic energy directive device such as a horn 59. The piston 46 is in sealing relationship with the cylindrical bore 52 and provides a fluid seal for the other end of the housing 51. The horn 59 is concentrically mounted to the mounting flange 57 of the housing 51 and is fastened to the housing 51 as by bolts 58. The horn 59 provides for directivity of acoustic energy generated by the hydroacoustic impulse generator 30.

The anvil 47 includes a shank portion 61 which fits tightly within the cylindrical bore 52 but is slidable along the longitudinal axis of the cylindrical bore 52 for transmitting impact energy which may be deliverable by the piston 46. interposed between the shank portion 61 of the anvil 47 and the end plate 54 is a shock isolating disc of shock-absorbing material such as a hard fiber. The shank portion 61 of the anvil 47 includes a shoulder 62 for limiting the travel of the piston 46 in the backward direction. The anvil 47 includes a piston guide portion 63 for guiding the piston 46 along the longitudinal axis of the cylindrical bore 52. The anvil 47 includes channels 64 and 64a for the flow of fluid into and out of the hollow piston 46 and the cylindrical bore 52 respectively for positioning the piston 46 in the cocked position. The channel 64 extends through the removable end plate 54 to the piston inlet line 33.

The piston 46 includes a thin cylindrical resilient wall portion 65, having a foot portion 66 in sliding relationship with the cylindrical bore 52 and a piston head portion 67 connected to the wall portion 65. The piston 46 defines a variable chamber 68, together with the piston guide portion 63 of the anvil 47. The foot portion 66 coacts with a piston stop on the housing 51 for locating the piston 46 in the cocked position.

The hydoracoustic impulse generator 30 further includes .a clamping means 71 for clamping the piston 46 in the cocked position as shown in FIG. 3. The clamping means 71 includes an annular recess chamber 72 which encircles the wall portion of the piston 46. The annular recess chamber 72 is in sealing relationship with the wall portion 65 of the piston 46 by two 0 rings 73 and 74 which are disposed in annular grooves 75 and 76 respectively. The clamping means 71 is connected to the inlet line 32 for communicating fluid pressure to the chamber 72. The fluid pressure and vacuum source 34 deliver a fluid pressure of sufficient magnitude to compress the wall portion 65 of the piston 46 against the anvil 47 and thus clamp the piston 46 in the cocked position. The clamping means 71 thus differs from the clamping means 21 of the hydroacoustic impulse generator 10 of FIG. 1 in that the sleeve 23 has been eliminated.

The hydraulic circuit of the hydroacoustic impulse generator 30 may be traced from the pressure and vacuum source 34 which supplies high pressure fluid through valve 38 to the inlet line 33 through the channels 64 and 64a to the chamber 68 and the cylinder 52. The chamber 68 and cylinder 52 may be evacuated through the channels 64 and 64a respectively to the inlet line 33 through the valve 41 to the inlet 36 of the fluid pressure and vacuum source 34.

The hydraulic circuit of the clamping means 71 may be traced from the annular chamber 72 through the inlet line 32 to valve 42 or valve 43 which selectively applies a high pressure fluid or a suction respectively in response to an electrical control signal from the fluid control circuit 44.

In the operation of the hydroacoustic impulse generator 7 30 (FIG. 3) the piston 46 is first moved into the cocked position by a high pressure fluid from the outlet 36 and clamped in the cocked position by the hydraulic clamping means 71 as shown in FIG. 3. When the piston 46 is in the cocked position, the valve 42 is in the open position and high pressure fluid may exist in annular chamber 72 such that the wall portion 65 is pressed against the anvil 47 and is maintained in this position by a radial frictional force. The radial frictional force is of suflicient magnitude to overcome the pressure head, P acting on the piston 46. The hydroacoustic impulse generator 30 is prepared for firing by closing valve 38 and opening valve 41 so that a partial vacuum may be drawn within chamber 68, the cylindrical bore 52 and channels 64 and 64a. That is the pressure which now exists within the chamber 68 and cylinder 52 is below the ambient pressure head P of the ambient fluid medium at which the hydroacoustic impulse generator 30 is located. The hydroacoustic impulse generator 30 is now ready for operation and for generating acoustic impulse energy in a fluid medium such as the sea or ocean.

The hydroacoustic impulse generator 30 may be fired by closing valve 42 and opening 43. The respective closing and opening of the valves 42 and 43 causes an in stantaneous reduction of pressure within chamber 72 and causes the piston 46 to be released from the cocked position. The pressure head P or ambient sea pressure acting on the piston 46 drives the piston towards the shoulder portion 62 of the anvil 47.

The piston 46 is accelerated towards the shoulder portion 62 of the anvil 47 by the pressure dilference which exists between the pressure head P as determined by the depth at which the hydroacoustic impulse generator 30 is operated and the partial vacuum which exists Within the chamber 68 and cylindrical bore 52.

The hydroacoustic impulse generator 30 may be reset into the firing position by closing valve 41 and opening valve 38 so that high pressure fluid, acting against the piston 46, will drive the piston outwardly into the cocked position. When the piston 46 is disposed in the cocked position, valve 43 may be closed and valve 42 may be opened so that high pressure fluid is admitted into the chamber 72. The high pressure fluid within the chamber 68, as was mentioned previously, compresses the thin wall portion 65 against the anvil 47 and clamps the piston 46 in the cocked position. When the piston is clamped in the cocked position, valve 38 is closed and valve 41 is open so that a partial vacuum may be drawn within the chamber 68 and the cylindrical bore 52. The hydroacoustic impulse generator 30 is now in the firing position and may be operated in the above-described manner.

FIG. 4 shows another embodiment of the invention in a hydroacoustic impulse generator 80 which differs from the hydroacoustic impulse generator 30 of FIG. 3 in that the hydroacoustic impulse generator 80 includes a spherical shaped housing 81 instead of a cylindrical housing 51. The spherical housing 81 provides a spherical battle which constitutes a rigid baflie which may provide a minimum amount of ringing and spurious vibrations which may be transferred to the ambient fluid medium. The hydroacoustic impulse generator 80 shown in FIG. 4, aside from the housing 81, is similar in structure and operation as the hydroacoustic impulse generator 30 of FIG. 3.

While specific embodiments of the invention have been described and shown, these may be considered illustrative. Still further modifications will undoubtedly occur to those skilled in the art. Therefore, the foregoing description is to be considered as illustrative.

What is claimed is:

1. An apparatus for generating acoustic energy in a fluid medium when submerged in said fluid medium, said apparatus comprising:

(a) a housing including a cylindrical cavity of a given length opened at one end to said fluid medium,

(b) a piston slidably disposed within said cavity and defining a chamber within said housing,

(c) clamping means for clamping said piston at said open end of said cylindrical cavity,

((1) means for evacuating said chamber to a pressure below the ambient pressure of said medium to which said housing end is exposed, and

(e) control means connected to said clamping means for selectively releasing said piston.

2. The invention defined in claim 1 wherein said housing is spherical in shape.

3. The invention defined in claim 1 further including a horn coaxially fixed to said open end of said housing.

4. The invention defined in claim 1 further including an anvil disposed within said cylindrical cavity proximal to the other end of said cylindrical cavity.

5. The invention defined in claim 1 further including a shock mounted anvil disposed within said cylindrical cavity proximal to the other end of said cylindrical cavity.

6. A hydroacoustic impulse generator for generating acoustic energy in a fluid medium when submerged at a given depth in said fluid medium, said generator comprising:

(a) :a housing having a cylindrical cavity opened at one end to said fluid medium,

(b) a piston adapted to slide within said cavity in a sealing relationship therewith,

(c) clamping means coupled to said housing for clamping said piston at said open end of said cylindrical cavity,

(d) means connected to said housing for evacuating said cavity, and

(e) control means coupled to said clamping means for selectively releasing said piston.

7. A hydroacoustic impulse generator for generating acoustic energy in a fluid medium when submerged at a given depth in said fluid medium, said generator comprising:

(a) a housing having a cylindrical cavity of a given length,

(b) a piston slidably disposed in said cavity and defining a chamber whose volume varies when said piston is moved along the length of said cavity,

(c) clamping means for clamping said piston at a given point along the length of said cylindrical cavity,

(d) means for evacuating said chamber to a lower pressure than that which exists in said fluid medium at said given depth, and

(e) control means connected to said clamping means for selectively releasing said piston from said given point.

8. A hydroacoustic impulse generator for generating acoustic energy in a fluid medium when submerged at a given depth in said fluid medium, said generator comprising:

(a) a housing including a cylindrical cavity having an open end exposed to said fluid medium,

(b) a piston slidably disposed Within said cavity for defining a chamber having a given volume when said piston is disposed in said given open end of said cavity,

(0) pumping means connected to said cavity for sliding said piston outwardly to said open end of said cavity,

(d) hydraulic means connected to said pumping means for clamping said piston in said open end of said cavity,

(e) means for evacuating said chamber, and

(f) control means coupled to said hydraulic clamping means for selectively releasing said piston.

9. A hydroacoustic sound generator comprising:

(a) a housing having a cylindrical bore, said housing including an anvil portion enclosing one end of said cylindrical bore of said housing and a piston stop at the other end thereof,

(b) a piston slidably disposed within said bore in said housing to define .a chamber within said housing, (c) pumping means for selectively applying a fluid under pressure for moving said piston outwardly to said piston stop,

(d) clamping means connected to said pumping means for clamping said piston when said piston is disposed at said piston stop,

(e) suction means for evacuating said chamber in said housing until a partial vacuum exists in said chamber, and

(f) means for selectively releasing said piston whereby said piston moves inwardly in response to an external pressure applied to said piston.

10. A hydroacoustic impulse generator for generating acoustic energy in a fluid medium when submerged at a given depth in said fluid medium, said generator comprising:

(a) a housing including a cylindrical cavity having an open end exposed to said fluid medium,

(b) a piston slidably disposed within said cavity for defining a chamber having a given volume when said piston is disposed in said given open end of said cavity,

(c) a shock mounted anvil interposed between said piston and said housing in said cavity,

(d) fluid pumping means connected to said cavity for sliding said piston outwardly to said open end of said cavity,

(e) hydraulic means connected to said pumping means for clamping said piston in said open end of said cavity,

(f) means for evacuating said chamber to a given low pressure below the ambient pressure of said medium at said given depth, and

(g) control means coupled to said hydraulic clamping means for selectively releasing said piston whereby said piston moves inwardly in response to the fluid pressure which exists at said given depth in said fluid medium.

References fitted by the Examiner UNITED STATES PATENTS 2,552,970 5/1951 Horsley 181 2,961,639 11/1960 Atanasofl 34014 3,056,104 9/1962 De Kansky 3409 X CHESTER L. J USTUS, Primary Examiner.

G. M. FISHER, Assistant Examiner. 

1. AN APPARATUS FOR GENERATING ACOUSTIC ENERGY IN A FLUID MEDIUM WHEN SUBMERGED IN SAID FLUID MEDIUM, SAID APPARATUS COMPRISING: (A) A HOUSING INCLUDING A CYLINDRICAL CAVITY OF A GIVEN LENGTH OPENED AT ONE TO SAID FLUID MEDIUM, (B) A PISTON SLIDABLY DISPOSED WITHIN SAID CAVITY AND DEFINING A CHAMBER WITHIN SAID HOSING, (C) CLAMPING MEANS FOR CLAMPING SAID PISTON AT SAID OPEN END OF SAID CYLINDRICAL CAVITY, (D) MEANS FOR EVACUATING SAID CHAMBER TO A PRESSURE BELOW THE AMBIENT PRESSURE OF SAID MEDIUM TO WHICH SAID HOUSING END IS EXPOSED, AND (E) CONTROL MEANS CONNECTED TO SAID CLAMPING MEANS FOR SELECTIVELY RELEASING SAID PISTON. 